1. Field of the Invention
The present invention relates to a telescopically collapsible energy absorbing steering column for motor vehicles.
2. Description of Related Art
Automotive designers have proposed a plethora of devices intended to "manage" or absorb the kinetic energy acting during the secondary collision of a vehicle operator with the vehicle's steering wheel. One early example of such a device is disclosed in U.S. Pat. No. 1,791,001, in which a spring loaded telescoping steering shaft has a slotted keyway section permitting both telescoping action and transmission of steering torque.
Shearable fasteners have been used to secure several of the components included in steering column energy absorption systems. U.S. Pat. No. 3,805,636 discloses an upper steering column mounting bracket attached to a body mounted bracket with shearable fasteners. U.S. Pat. No. 3,899,937 discloses a shearable fastener for attaching upper and lower steering column outer tubes together. Finally, U.S. Pat. No. 3,921,747 discloses yet another shearable element for attaching an upper steering column mounting bracket to an automotive body.
Plastically deformable structures have found great favor among steering column designers. U.S. Pat. No. 3,505,897 discloses a plastically deformable sheet metal structure for connecting a steering column to body mounted brackets. Plastically deformable bracketry for attaching upper steering column mounts to automotive bodies are also shown in U.S. Pat. Nos. 3,600,971, 3,785,671, 3,803,938, 3,815,437, 3,855,876, 4,194,411 and U.S. Patent Office Defensive Publication No. 743678. U.S. Pat. No. 4,000,876 discloses yet another arrangement in which prestressed elastomeric sleeves are compressed to absorb energy caused by longitudinal displacement of a steering column.
The energy absorbing steering column of the present invention utilizes both shearable fasteners attaching upper and lower steering column tubes and a plastically deformable upper column tube body mounting bracket to absorb the energy of secondary collisions.